1. Field of the Invention
The present invention relates to an imaging apparatus. More specifically, the present invention relates to an imaging apparatus such as a copier or a printer, and particularly relates to an apparatus capable of outputting color images.
2. Background Information
Copiers, printers, and other such imaging apparatuses are known in conventional practice. These imaging apparatuses are provided with a developer unit that performs developing by allowing toner to adhere to an electrostatic latent image formed on the surface of a photoreceptor drum. The toner is stored inside the developer unit, and the developer unit includes a stirring roller for stirring the toner, and a developing roller or the like for supplying the toner to the surface of the photoreceptor drum.
After an imaging apparatus having this type of configuration is manufactured in a factory, the imaging apparatus takes on one of the following three primary aspects during the shipping stage. Specifically, the three aspects are as follows: the toner is not stored in the developing unit and an image check is not made; the developing unit is removed from the imaging apparatus after toner is loaded into the developing unit and an image check is made, and the developing unit is mounted on the imaging apparatus after the developing unit is cleaned by blowing air through the inside of the developing unit; or the toner is stored in the developing unit and an image check is made, but the developing unit is not cleaned.
When a nonmagnetic toner component is stored in the developing unit, selective developing takes place in which small toner particles are preferentially consumed as specified small toner particles, and large toner particles accumulate in small portions inside the developing unit as more and more pages are printed. Consequently, the particle size distribution of the toner stored inside the developing unit changes every time the toner is newly replenished. In this developing unit, when the toner is stirred by the stirring roller, contact among the toner particles causes stress within the toner, and external toner additives are shed from the toner surface and are incorporated into the toner.
These changes in the particle size distribution of the toner stored in the developing unit, as well as toner degradation due to contact among the toner particles cause concentration reduction and surface fogging in the images printed on the recording paper, resulting in the reduced quality of the images. In particular, the problems resulting from changes in the particle size distribution of the toner or degradation of the toner occur more rapidly with a reduction in the toner storage capacity of the developing unit. To maintain the quality of the images printed on the recording paper, a refreshing operation is performed at a specific timing interval. In this operation, old toner stored in the developing unit is replaced with new toner.
One proposed example of an apparatus in which the developing unit is refreshed is an imaging apparatus in which the toner is formed into a uniformly thin film by charging to maintain a constant particle distribution in the toner on the surface of the developer sleeve, and in which image concentration reduction, surface fogging, and other image problems are prevented. This is accomplished by a method in which an alternating-current electric field is applied between the photoreceptor drum and a developer sleeve for conveying toner to the developing area on the photoreceptor drum, and the toner remaining on the surface of the developer sleeve is scattered over the photoreceptor drum to refresh the developer sleeve when the average printing density for a standard number of printings falls below a specific value (see Japanese Laid-open Patent Application No. 2000-330379).
However, problems are encountered in that an image check cannot be made in cases in which the apparatus is designed so that the toner is not stored in the developing unit and an image check is not made when shipped from the manufacturing plant. Furthermore, not only is time needed to attach and remove a developing unit, but there is also the possibility of assembly errors caused while the developing unit is attached or removed in cases in which the apparatus is designed so that the developing unit is removed from the imaging apparatus after toner is stored in the developing unit and an image check is made, and the developing unit is mounted in the imaging apparatus after the developing unit is cleaned by blowing air through the inside of the developing unit. The frequency of assembly errors increases particularly when the configuration of the imaging apparatus becomes more complicated as the apparatus is reduced in size.
Furthermore, there is a possibility that condensation will adhere in the toner remaining inside the developing unit due to variation in the outside temperature, or that the toner remaining inside the developing unit will scatter to the outside of the developing unit due to vibrations while the imaging apparatus is being transported in cases in which the apparatus is designed so that toner is stored in the developing unit and an image check is made, but the developing unit is not cleaned. Consequently, the imaging apparatus is preferably shipped after toner is stored in the developing unit, an image check is made, and the toner is completely removed from the developing unit while the developing unit remains mounted in the imaging apparatus.
The toner disposed closer to the stirring roller in the portion where the toner is stored in the developing unit is stirred in the circumferential direction, while toner farther from the stirring roller is pushed towards the inner wall of the developing unit when information is printed on recording paper. Specifically, a phenomenon occurs wherein toner closer to the stirring roller flows through the inside of a tunnel formed as a result of the fact that the toner farther from the stirring roller is pushed towards the inner wall of the developing unit. In cases in which the developing unit is provided with a conveying spiral for causing the toner to adhere uniformly to the surface of the developing roller by conveying the toner in the axial direction of the developing roller, the toner conveyed in a constant direction by the rotation of the conveying spiral is pushed towards the inner wall of the developing unit.
The pushing of the toner towards the inner wall of the developing unit causes the toner to enter the dead space in the portion where the toner is stored in the developing unit, and the toner remains in this dead space. The term “dead space” refers to a location in the portion where toner is stored in the developing unit and where the toner is not supplied to the photoreceptor drum. Consequently, old toner cannot be completely removed from the developing unit even though an operation is performed to remove the toner from the developing unit after the toner is stored in the developing unit and an image check is made during shipping of the imaging apparatus from the manufacturing plant.
Also, old toner cannot be completely removed from the developing unit even if a refreshing operation is performed to replace the old toner in the developing unit with new toner at a specific timing interval as described above. Therefore, the new toner is mixed with the old toner in the developing unit after the refreshing operation, and the image quality reduction that accompanies toner degradation due to changes in the toner particle size distribution or due to contact among the toner particles is manifested at an earlier stage than when new toner is stored in the developing unit. Consequently, the intervals between refreshing operations intended to prevent reduction in image quality grow shorter as printing continues, leading to problems related to the reduced service life of the toner stored inside the developing unit.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved imaging apparatus. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.